1. Field of the Invention
This invention relates to a method and apparatus for transmitting an electromagnetic pulse. In one aspect, the invention relates to an electromagnetic pulse generator and a plasma antenna generator capable of forming a plasma antenna for reradiating an electromagnetic pulse from the electromagnetic pulse generator.
2. Description of the Related Art
Electromagnetic energy can be used in many ways to sense or affect objects from a distance. Radar, for example, is reflected electromagnetic energy used to determine the velocity and location of a targeted object. It is widely used in such applications as aircraft and ship navigation, military reconnaissance, automobile speed checks, and weather observations. Electromagnetic energy may also be used to jam or otherwise interfere with radio frequency transmissions or to affect the radio transmitting equipment itself.
In certain situations, it may be desirable to radiate one or more electromagnetic pulses over an area to sense or affect objects within the area. Generally, as illustrated in FIG. 1, a signal generator 102 generates an electromagnetic pulse, which is radiated by an antenna 104 as an electromagnetic wave 106. Upon encountering an interface, such as an interface between an object 108 and the air 110, a portion of the energy of the wave 106 is reflected as an electromagnetic wave 112. The reflected wave 112 may then be received by a sensor 114, which analyzes the reflected wave 112 to determine various characteristics of the object 108.
It is often desirable to deploy such antennas, e.g., the antenna 104, during flight. For example, a spacecraft approaching a planetary body may deploy an antenna so that electromagnetic energy may be directed toward the surface of the body. Conventional antennas generally include rigid or semi-rigid members that may be compactly folded for storage and transport and then unfolded when needed. Alternatively, conventional antennas may be wires that are explosively deployed or deployed by parachutes. A substantial amount of time is often required to deploy such antennas, which results in additional planning to determine the appropriate time to begin deployment so that the antenna will be available when needed. Further, circumstances may arise in which the immediate transmission of electromagnetic energy is desirable. If the antenna has not been deployed, there may not be sufficient time to deploy the antenna and transmit the electromagnetic energy in the desired time frame.
It may also be desirable in certain situations to transmit electromagnetic energy having a broad spectrum of frequencies or to transmit low frequency electromagnetic energy. Generally, longer antennas are capable of transmitting electromagnetic energy more efficiently at lower frequencies than shorter antennas. Such longer antennas may typically be capable of transmitting electromagnetic energy having higher frequencies as well. Longer foldable antennas require more storage space, may be more complex, and generally take longer to unfold.
The present invention is directed to overcoming, or at least reducing, the effects of one or more of the problems set forth above.